Canine infectious laryngotracheitis virus, an adenovirus designated CAV-2, induces numerous changes in the nucleus and cytoplasm of canine kidney cells (MDCK). The following features could be observed on ultrathin sections examined in the electron microscope: a shift of the nucleolus towards the nuclear membrane and a compression of the latter by the virus particles; the release of virions into the cytoplasm following the tearing or evagination of the nuclear membrane; the attachment of virus particles onto the numerous microtubules of the infected cell. Microfilaments appear to be involved into the vectorial movement of virus particles towards the cytoplasmic membrane in the final phase of infection.